What's the difference between PoolTcpConnector and SimpleTcpConnector ?

The main difference is that the Pool connector will create a pool of simple connectors, allowing the server to answer to more requests at the same time, while a simple connector can anwer only a response at a time.

The simple connector hasn't been designed to be used unless you know that you will process only a request at a time.

You can use it, for example, if you are running Tomcat under Apache, using mod_jk. In that case Apache talks with tomcat using the Apj13 protocol, and you need only one connector listening with the Ajp12 protocol for shutting down Tomcat. In that case using a pool would be a waste of resources.